Centrifugal blowers typically include impellers having a plurality of blades that redirect an incoming airflow toward a radial direction as the airflow moves from the impeller inlet to the impeller outlet. The blades are typically attached to a hub for rotation therewith. The hub typically defines an airflow surface on the base of the impeller to help redirect the incoming airflow.
In automotive climate control applications (i.e., heating, ventilation, and air conditioning), centrifugal impellers may be generally grouped into two categories: a) low cost, one-piece impellers; and b) higher cost, higher efficiency, two-piece impellers. One-piece impellers, because of their lower cost, are generally more prevalent in automotive climate control applications than two-piece impellers. Two-piece impellers are generally used in an automotive climate control application when the need for high efficiency or high pressure capability outweighs any cost disadvantage.
Further, in automotive climate control applications, centrifugal blowers should operate efficiently over a range of operating conditions. For example, duct passages open and close to direct air through different heat exchangers of different flow resistances. Flow resistance typically is greatest in heater and defrost conditions, and least in air conditioning mode. In some instances, the high flow resistance during heater and defrost modes can cause performance and/or noise problems for conventional one-piece impellers, which may be less efficient than the more expensive two-piece impellers, or only capable of producing relatively low pressures compared to the more expensive two-piece impellers.